Re: Auto-tuning work_mem and maintenance_work_mem

Bruce,

>> That's way low, and frankly it's not worth bothering with this if all
>> we're going to get is an incremental increase.  In that case, let's just
>> set the default to 4MB like Robert suggested.
> 
> Uh, well, 100 backends at 6MB gives us 600MB, and if each backend uses
> 3x work_mem, that gives us 1.8GB for total work_mem.  This was based on
> Andrew's concerns about possible over-commit of work_mem.  I can of
> course adjust that.

That's worst-case-scenario planning -- the 3X work-mem per backend was:
a) Solaris and
b) data warehousing

In a normal OLTP application each backend averages something like 0.25 *
work_mem, since many queries use no work_mem at all.

It also doesn't address my point that, if we are worst-case-scenario
default-setting, we're going to end up with defaults which aren't
materially different from the current defaults.  In which case, why even
bother with this whole exercise?

-- 
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com